The proposed work will involve the synthesis of molecules designed to trigger long-lived, adaptive immune responses that are protective against infection caused by the Gram-negative coccobacillus Acinetobacter baumannii. There are presently no approved vaccines for A. baumannii, and there has been an increasing incidence of infections caused by drug-resistant strains. Central Hypothesis: Covalent conjugation of synthetic portions of an Acinetobacter baumannii lipooligosaccharide (LOS) to the Bacteroides fragilis capsular polysaccharide A1 (PSA1) will result in molecules that can trigger adaptive immune responses selective to A. baumannii. Project Goals: Short-term goals include synthesis of A. baumannii LOS-PSA1 conjugates and their injection into mice to determine their efficacy in prevention of infections caused by A. baumannii. Long-term goals include the development of a vaccine and the development of monoclonal antibodies to be used as a therapeutic. Specific Aims: Specific Aim 1: Synthesis of A. baumannii LOS core oligosaccharides that can be conjugated to PSA1 and other carrier molecules. The success of this Specific Aim will lie in the effective implementation of synthetic strategies and completion of target molecules. Specific Aim 2: Conjugation of the A. baumannii LOS core oligosaccharides to PSA1 and subsequent injection into mice followed by studies to determine immunogenicity and protective effects against A. baumannii infection. The immunogenicity and protective effects of the LOS-PSA1 conjugates against bacterial challenge with A. baumannii will be studied. The success of this Specific Aim will lie in the effective protection of mice against infection by A. baumannii in which long-lived, adaptive immunity has been triggered. Specifc Aim 1 studies will involve the multistep chemical synthesis of a series of five oligosaccharides with varying complexity and which are based on an A. baumannii LOS core structure. The 4-aryl-3- butenylthioglycosides undergoing development in our laboratory will be critical intermediates in these syntheses. Other key features include synthetic strategies to generate an alkoxyamine-bearing linker that will be used to conjugate the oligosaccharides to PSA1. Specific Aim 2 studies will start with the condensation of the aforementioned alkoxyamine-bearing oligosaccharides with aldehydes generated through the oxidative cleavage of a diol moiety on PSA1. The resulting LOS-PSA1 conjugates will be injected into mice and the mouse anti-sera will be collected subsequently. The immunogenicity of the LOS-PSA1 conjugates will be determined through ELISA assays to determine the nature of the antibody response as well as flow cytometry to determine if the antibodies bind to A. baumannii in addition to an assay to determine the bactericidal effects of the sera. Pending the results of the initial serological experiments, bacterial challenge experiments in which bacterial dissemination and survival rates in mice are determined will be conducted. Such experiments will be conducted with the most promising LOS-PSA1 conjugates based on the initial serological experiments.